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Physics > Atmospheric and Oceanic Physics

Title:
On climate response to changes in the cosmic ray flux and radiative budget

Abstract: We examine the results linking cosmic ray flux (CRF) variations to global
climate change. We then proceed to study various periods over which there are
estimates for the radiative forcing, temperature change and CRF variations
relative to today. These include the Phanerozoic as a whole, the Cretaceous,
the Eocene, the Last Glacial Maximum, the 20th century, as well as the 11-yr
solar cycle. This enables us to place quantitative limits on climate
sensitivity to both changes in the CRF, Phi_CR, and the radiative budget, F,
under equilibrium. Under the assumption that the CRF is indeed a climate
driver, we find that the sensitivity to CRF variations is consistently fitted
with mu := -Phi_0 (dT_global/ d Phi_CR) = 6.5 +/- 2.5 K (where Phi_0 is the CR
energy flux today). Additionally, the sensitivity to radiative forcing changes
is lambda := dT_global/ dF_0 = 0.35 +/- 0.09 K/(W/m^2), at the current
temperature, while its temperature derivative is negligible with d lambda /
dT_0 = 0.01 +/- 0.03 1/(W/m^2). If the observed CRF/climate link is ignored,
the best sensitivity obtained is lambda = 0.54 +/- 0.12 K/(W/m^2) and d lambda
/ dT_0 = -0.02 +/- 0.05 1/(W/m^2). The CRF/climate link therefore implies that
the increased solar luminosity and reduced CRF over the previous century should
have contributed a warming of 0.37+/-0.13 K, while the rest should be mainly
attributed to anthropogenic causes. Without any effect of cosmic rays, the
increase in solar luminosity would correspond to an increased temperature of
0.16+/-0.04 K.